Rotary tabletting machines, as they are described in the EP 0 572 816, comprise a matrix disk rotatably driven around a vertical axis which matrix disk includes matrix bores arranged on a circle. To said matrix bores upper and lower punches are associated which are rotating in synchronism with the matrix disk and compress pulverized material filled into the matrix bores. The punches are actuated by suitable control cams for selectively setting free the matrix bores and carrying through the compressing procedure, respectively. During filling in a filling station, the lower punch is arranged in a lower position within the matrix bore, while the upper punch is spaced apart from the matrix disk.
The compression of many substances makes a lubricant or parting compound necessary for preventing the tablet from bonding to the pressing tools as well as too a high friction while ejecting the tablet from the matrix bores. It has become known to use magnesium stearate as a pulverized parting compound. From the DE 38 11 261 it also has become known to use liquids finely dispersed in gases.
It has become known to finely disperse the lubricant in the material to be compressed, e.g. by adding or spraying magnesium stearate on the material to be compressed. Thereat the amount of lubricants is 0.5 to 1% of the material to be compressed. The relatively high concentration of the lubricant is necessary for providing on the surface of the tablet a sufficient quantity of said lubricant so as to prevent the tablet from bonding to the tool. In many cases, however, such a high concentration of lubricants is not desirable.
Another possibility is to deposit the lubricant on the matrix bore and lower punch, for instance by a clock-pulse blowing, as described in the DE 38 11 260. A Venturi nozzle is arranged in a tabletting machine directly in front of the punch and the matrix opening. A controlled compressed-air supply serves the purpose of blowing off so-called powder packages on the used surfaces. The known device involves quite some expenditure, especially with respect to the control system, and there is a risk that too a big quantity of the lubricant is discharged which then is deposited on the surfaces adjacent to the matrix bore and the punch shafts in an undesired way. Besides, the known method can be carded out at relatively low speeds only.